Pensions and Other Postretirement Benefits - Pension and Postretirement Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits
Components of Net Periodic Cost:
Service Cost	$ 3.9	$ 3.3
Interest Cost	4.6	11.5
Administrative Expenses	0.1	0.1
Expected Return on Plan Assets	(6.9)	(13.8)
Net Settlement/Curtailment Loss	152.5	0.0
Amortization:
Prior Service Credit	0.0	0.0
Actuarial Loss (Gain)	1.6	2.5
Net Periodic Cost (Benefit)	155.8	3.6
Postretirement Health Care Benefits
Components of Net Periodic Cost:
Service Cost	0.1	0.1
Interest Cost	0.2	0.4
Administrative Expenses	0.0	0.0
Expected Return on Plan Assets	0.0	0.0
Net Settlement/Curtailment Loss	0.0	0.0
Amortization:
Prior Service Credit	(0.1)	(0.1)
Actuarial Loss (Gain)	(0.4)	(0.5)
Net Periodic Cost (Benefit)	$ (0.2)	$ (0.1)